Intracoronary Implantation

Intracoronary Implantation of Radioactive Stent
Restenosis has been the Achilles’ heel of coronary interventions. Intracoronary stenting has improved catheter based revascularisation of obstructive coronary artery disease. Despite the improved outcomes with stenting, restenosis occurs at a high rate, especially in smaller vessels and in longer lesions.

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Recently, the use of ionising radiations received much interest as a new treatment tool to reduce restenosis after coronary angioplasty. In recent years numerous animals experiments and feasibility clinical pilot trials have demonstrated that low doses of radiation when applied during coronary intervention reduce neointimal proliferation, prevent vessel contraction and alter the restenosis rate.

There are two main approaches for delivering endovascular radiation. One is based on gamma or beta source with very high activities to be delivered at site through a catheter, in a limited period of time. The other approach is based on a stent rendered radioactive for long exposure and continuous low dose treatment.

Radioactive stents deliver ionising radiation at very low dose rates according to the half life of the incorporated radiosotopes. The activity levels of radioactive stents are upto 10,000 times lower than activity levels of sources used for catheter based vascular Brachytherapy, They allow uniform dose distribution with precise dosimetry because of direct source contact with the circumference of the vessel.Radioactive stents have been produced by cyclotron activation, ion implantation and proton bombardment for both beta, gamma and combination isotopes. Iridium 192 is the isotope used for gamma radiation and p32 is used for beta radiation. p32 is a pure particle emitting radioisotope and has a short half–life (14.3 days) and a limited range of tissue penetration (3–4mm) It is the radioactive isotope being used in the Isonipsi trial to assess the role of beta radiation in reducing the rate of restenosis. Ruby Hall Clinic is one of the centres recognised for the trial. We have herein reported the first case of radioactive stent implantation in a native coronary artery in Pune. A 59 year old male with strong Family H/o IHD was offered a ‘Radiated Stent’ on 1st of Jan.1999 at Ruby Hall Clinic, the first such procedure for the city of Pune. He had MI two months back, was having post–MI angina and positive Exercise test. His angio showed a tight lesion in segment II or LAD, a single vessel disease with type A lesion. A Medtronics BE stent was coated with Beta radiation p32 and deployed at the lesion site in a conventional fashion with moderately high pressure deployment. The radiation with this kind coating spreads to about 5mm from the metal edges. Post angioplasty, patients remains totally symptom free and has a normal stress test. A review Coronary Angiogram in August 1999 shows normal stent appearance with no norrowing.

Initial impressions from the pre–clinical work and the experience gained so far from the feasibility and the Phase I clinical trials may lead to the conclusion that vascular Brachytherapy is breakthrough adjunct therapy to vascular intervention. However large scale clinical randomised trials are required to support the safety and effectiveness of this technology and several key issues still need to be addressed such as the ideal dose, adjunctive therapy with radioscusitizers and late radiation effects on patients.

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